1. Attention: We have put together a thread with tips and a tutorial video to help with using the new software. Please take a moment to check out the thread here: Trapshooters.com Tutorial & Help Video.
    Dismiss Notice

How far off?

Discussion in 'Shooting Related Threads' started by GrandpasArms, Oct 13, 2011.

Thread Status:
Not open for further replies.
  1. GrandpasArms

    GrandpasArms Active Member

    Joined:
    Nov 11, 2010
    Messages:
    872
    Location:
    About 40 miles west of Chicago, IL
    I had been pleased with my 34" BT99. Because of some neck/shoulder pain I decided to raise the rib so I'd shoot more "heads up". I added a rib (3/4 inch) and had an adjustable comb fitted so I could increase its height by the same amount.

    Upon patterning I discovered it shoots 6 to 10 inches to the left. That may explain a few things. Regardless, the reason for this post is to discover how far I might have botched the job to make the gun now shoot so far left at 35 to 40 yards. The rib looks correct and it feels like it is centered o the original rib.

    I can adjust the comb and I've done so. I'm just wondering if there is some math relationship between comb offset and shifting the pattern.

    Larry
     
  2. open choke

    open choke TS Member

    Joined:
    Sep 12, 2011
    Messages:
    406
    Maybe if you're head being more erect changed the shape of your comb placement. That may throw your pattern off so off set the comb to the right and see if the pattern goes more in the middle.

    My gun patterned slightly to the left so I have my comb shifted a bit to the right.

    I know a guy who needs to have his comb shifted quite a bit to the right that he is having a custom comb made with is carved out extra to even it out on the stock so its not so far to one side.
     
  3. wolfram

    wolfram Well-Known Member

    Joined:
    Jul 17, 2007
    Messages:
    6,258
    Could be a matter of canting the gun?
     
  4. BigM-Perazzi

    BigM-Perazzi Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    8,542
    Location:
    HELL, MICHIGAN
    As I remember(scratches head), figure 1/16" for every inch offline...
     
  5. waverider

    waverider Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    1,623
    Location:
    HI
    Good enough for government work...1/16" = 1 inch at 16 yards or 1/16 = 2 inches at 32 yards.

    This was most likely with a 25" barreled SxS.

    There is a math formula based on exact distance from eye to front bead and front bead to target.

    Jason
     
  6. MKillian

    MKillian TS Member

    Joined:
    Sep 7, 2011
    Messages:
    260
    <I>"Could be a matter of canting the gun?"</I>

    Wouldn't make one bit of difference with a top single.

    Try Neil Winston's method for finding POI:

    Install a full choke (if you have one). Use a standard trap load. Set up your target paper 13 yards away. Draw a big cross on the paper and aim for the center of it. Fire from a bench rest. The pellets will make a clean hole in the paper from this distance. Measure the location of the center of the hole relative to both lines of the cross and multiply by 3. That will be your point of impact at 39 yards.

    Here's the full thread: <I>http://www.trapshooters.com/noframes/cfpages/thread_archive2.cfm?threadid=172562</i>

    Mike K
     
  7. wolfram

    wolfram Well-Known Member

    Joined:
    Jul 17, 2007
    Messages:
    6,258
    Sorry Mike but a serious cant will effect the POI. Doesn't just apply to a certain type of shotgun or just to shotguns for that matter.

    Neil's POI method is a good measure of where the gun will hit assuming you always shoot from the bench and aim the thing like a rifle - not really how most of us shoot clays.
     
  8. MKillian

    MKillian TS Member

    Joined:
    Sep 7, 2011
    Messages:
    260
    With the sight plane being as close to the bore as it is, you would have to turn the gun on it's side mess up the POI. Then the most the gun could be off would be the distance of the POI above the sight plane. Maybe an issue for an unsingle that shoots 24" high but hardly for a BT-99. Remember we're talking about a 12"-18" effective shot cluster at 35-40 yards. A few degrees of cant won't make a noticeable difference in the POI. Here are some photos to illustrate: <I>http://www.trapshooters.com/cfpages/thread.cfm?Threadid=242640&ShowDeleted=Yes&SortBy=ASC</I>

    Shooting from a bench is the only way to determine whether the gun or the shooter is causing the POI to be off! I've seen many guns that shoot true from the bench but shoot off target when shot off-hand because of the way the shooter handles the gun.

    Mike K
     
  9. miketmx

    miketmx Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    2,964
    6 to 10 inches to the left should be noticeable with bore-sighting. Get a deprimed 12 GA empty to put in the chamber and open the gun and rest the forend on a picnic table while you look through the barrel and point at a distant object on the back fence. Now carefully raise your head without disturbing the gun and look down the rib at the same object. The POI error should be obvious without actually shooting the gun. The rib might be mis-aligned.
     
Thread Status:
Not open for further replies.